Homogenization is a long-used industrial process which aims, in a fatty emulsion such as milk, for example, to split the largest fat globules into smaller fat globules and thereby stabilize the fatty emulsion. For milk, for example, this means that creaming is prevented and the bulk of all consumer milk is nowadays homogenized.
The homogenization is usually carried out by mechanical processing, so that the fatty emulsion, which has a high input pressure, is forced to pass at high velocity through a very narrow gap, in which the fat globules of the fatty emulsion are broken up by the turbulence which is generated at high velocities and by cavitation bubbles which implode in the liquid. The process takes place for a very short period and what happens during this period is that the velocity of the fatty emulsion during passage increases as the pressure decreases, which causes the liquid to boil.
A homogenizer essentially consists of a large piston pump, which produces a high pressure, and a counterpressure device, in which the actual homogenization takes place. The counterpressure device or homogenizing valve in turn consists of a pressurized, resilient valve cone, a valve seat, as well as a wearing ring and a valve housing, which surround the valve cone and the valve seat. The valve cone and the seat are usually rotationally symmetric and arranged such that a radial constriction, which constitutes a homogenization gap, appears between these two parts. The height, width and length of the gap determine the volume at which the homogenization takes place. This volume must be sufficiently small to obtain an effective homogenization. The gap height is reduced in the event of a higher pressure upon the liquid which is to be homogenized, at the same time as a larger flow means that the gap height is increased.
Particularly in the homogenization of pasteurized milk, compared with UHT-treated milk, a lower pressure is employed, at the same time as it is wished to increase the flow quantity. This means that the homogenizing valve would need to be made larger, so that the gap height decreases, in order to obtain good homogenization at this lower pressure and increased flow. It has been shown, however, that an up-scaling of existing, well-functioning homogenizing valves does not always work especially well in practice. The larger the pressurized surface which is acquired, the greater are the forces generated and the larger must be the homogenizing valve. At the same time, the costs of such a homogenizing valve rise many times over.
Another way of solving the problem is to connect a number of homogenization gaps in parallel, as shown in European patent specification EP 034 675. In this way, an extension of the gap length, and thus a reduction in gap height, is obtained. This type of homogenizing valve with parallel-connected homogenization gaps has, however, a virtually fixed gap height. Without conversion, it permits only one flow and one homogenizing pressure. It also has the drawback that it wears in an uneven and uncontrollable manner, which adversely affects the homogenization result.